Trimming potentiometer



May 24, 1960 J. l.. KAssAY ETAL 2,938,186

TRIMMING POTENTIOMETER Filed Oct. 30, 1956 John L. Kassay, Gene M.LeFave, Alfred Mt. Stewart E Albert J. Barano tf.

Inventors.

A TTORNE Y.

United States Patent() TRn/IMING PornNrroMETER John L. Kassay, Yucaipa,Gene M. Le Fave and Alfred W. Stewart, Riverside, and Albert J.Baranotf, Santa Ana, Calif.; said Kassay assignor to Yucaipa InstrumentsLtd., Inc., Yucaipa, Calif., a corporation of California Filed Oct. 30,1956, Ser. No. 619,312

12 Claims. (Cl. 338-180) This invention relates to a trimmingpotentiometer and more particularly to a trimming potentiometer whichcan be fabricated in miniature sizes and easily assembled and which isalso easily convertible to a trimming resistor.

Trimming potentiometers of this type now in use require'that theresistance element and the leads be imbedded in a plastic material, suchas Bakelite, in order to be properly insulated. Such a constructionnecessitates the molding of the resistance element and leads into thesmall plastic body and and considerable diiiculty is encountered inproperly locating these components. Further, the wiper mounting must beconstructed of a plastic material, such as Bakelite, having a threadedopening to receive a threaded shaft and t-he threads are subject tobeing stripped at either end of the travel of the wiper if continuedpressure is exerted on the shaft. In addition, the mounting shaft is`provided with bearing surfaces in the Bakelite body which do not providea moisture seal for the instrument. Further, the resistance element ofsuch prior devices cannot be readily modified to utilize differentmaterial to obtain different lranges of resistance while utilizing thesame body construction.

By the present invention, a trimming potentiometer is provided in whichthe components can be assembled simply by dropping one after anotherinto place in the potentiometer body. The potentiometer body can beconstructed of anodized aluminum which provides increased mechanicalstrength and a hard ceramic insulation surface for insulation purposes.The aluminum body also has the characteristic of good heat dissipationwhich allows operation at much higher temperatures and power rating. Thebody can be constructed in body portions which are identical inconstruction and interchangeable so that only one body portion need beproduced to construct the complete potentiometer. The body portions areheld together by humidity resistant adhesive which provides both amechanical and moisture seal and moisture sealing means are provided forthe shaft. The sealing means for the shaft is preferably fabricated ofnylon which expands with increase in moisture content and still retainsgood lubricating properties.

The resistance unit of the present invention comprises a mounting boardwhich is received within one of the body portions land carries theresistance element. The use of the mounting board permits the use ofvarious types of resistance material with the same instrumentcomponents. For instance, the mounting board can be wire wound or stripsof carbon coated tape or thin, highly resistance metal can be mounted onthe board. The wiper assembly has two notched elements which engage athreaded shaft and at either end of the travel vof the wiper assembly,one element will skip the threads during continued rotation of theshaft, thus preventing stripping of the threads and jamming of the wiperassembly. Also, because of the fact that the notched elements serve asthe threads for the wiper assembly, the

r2,."l38,'l86 Patented May 24, 1960 wiper assembly can be incorporatedin the instrument by simply placing the assembly on the shaft.

'Ihe leads for the potentiometer are located Ain grooves within the bodyportions which are so located that the body portions are interchangeableand the leads can extend from either side of the instrument. Leads of atstrip material are utilized and thus, the leads can be easily replacedby printed circuitry attached by adhesive to the resistance unit. Sincethe output lead of the potentiometer extends the length of theresistance element, it is possible to utilize the instrument as atrimming resistor by simply placing one of the terminal leads and the'output lead in any given circuit and thereafter, the wiper assembly canbe adjusted to incorporate into the circuit the precise resistancedesired. Since the body portions are held together by a humidityresistant adhesive and the shaft is sealed against moisture, it ispossible to fill the interior of the instrument with a viscose, heatresistant oil so that the potentiometer is highly resistant to wear,noise, etc.

It is therefore an object of the present invention to provide a trimmingpotentiometer constructed of interchangeable body portions into whichthe elements can be simply dropped one after another and thereafter, thebody portions sealed together to provide the complete instrument.

Another object of the present invention is to provide an instrumenthousing formed of rigid material, such as aluminum, having good heatdissipation qualities and having a hard ceramic surface for insulationpurposes.

A further object of the present invention is to provide electricalconnections for a potentiometer so that the potentiometer can be easilyconverted to a trimming resistor.

Another object of the present invention is to provide a mounting memberfor the resistance element which can support a variety of resistancematerial, such as wire or strips of resistant material, without changingthe construction of the instrument.

A further object of the invention is to provide a wiper assembly havingnotched elements for engaging the threads on the shaft so that the wiperelements can be dropped onto the shaft and will skip the threads ateither end of the wiper assembly travel.

A further object of the invention is to provide a bearing and moisturesealing shaft head constructed of nylon or other suitable plasticmaterial which has inherent lubricating qualities.

These and other objects of the invention not specifically set forthabove will become readily apparent from the accompanying description anddrawings in which:

Figure 1 is a horizontal section of the trimming po tentiometer of thisinvention with the top body portion removed to illustrate the resistanceunit and the wiper assembly.

Figure 2 is a vertical section along line 2f-2 of Figure l showing thenotched elements of the wiper assembly positioned on the shaft andillustrating the sealing means for the shaft.

Figure 3 is a transverse vertical section along line 3--3 of Figure 2showing the Wiper contacts riding on the resistance element and theterminal leads positioned on the opposite side of the resistanceelement.

Figure 4 is a perspective view of the wiper assembly showing the springarm, the wiper contacts and the notched elements which engage the shaft.

Figure 5 is a partial vertical section similar to Figure 2 illustratinga modification of the sealing means for the shaft.

Figure 6 is a perspective view of a modification of the resistance unitwherein two strips of resistant material `are attached to the mountingboard and are connected to the' terminal leads by silver clipspositioned over the ends of the mounting board.

Figure 7 is a perspective View of another modilication of the resistanceunit wherein two strips are positioned on the mounting board and areconnected in series with the terminal leads.

Referring to Figures l and 2, the instrument housing comprises two bodyportions 10, 11 which are identical in construction. One end of eachbody portion has a semicircular cutout 12 having a larger semi-circularcutout 13 positioned intermediate its ends. When the body portions and11 are placed together, the cutouts 12 and 13 receive a cylindrical headmember 14 which has an enlarged rib 15 positioned in the circular spaceformed by the cutouts 13. The member 14 also has a circular opening 16into which knurled end 17 of shaft 18 is pressed. The member 14 also hasa notch 19 located exteriorly of the housing to provide for connectingthe shaft to any suitable type of rotating mechanism. The other end ofeach of the body elements contains a rectangular cutout 20 whichconnects with a semi-circular cutout 21, so that when the body portions10 and 11 are placed together, the semi-circular cutouts 21 form acircular opening for the Unthreaded end 22 of shaft 18. T he end 22contains a groove 23 and has a rounded end portion 24, both of which arelocated in the closed space formed by the cutouts Ztl when the bodyportions are placed together. This space also receives a channel shapedmember 25 constructed of spring metal and having a slot 26 for receivingthe groove 23 when the member is flexed inwardly. After the member 25 isreleased, the pressure of the member upon the end 24 serves tocontinually force the end 24 against the side of the opening formed bythe spaces 2t). Thus, the shaft 18 is held in fixed position within thehousing and the force on end 24 places a desirable drag upon shaft 18.The circular opening formed by the cutouts 13 is somewhat wider than therib 15 so that the member 14 does not have to be accurately located onthe end of the shaft.

Each body portion 10, 11 contains a rectangular cavity 27 so that whenthel body portions are placed together, a closed, interior, rectangularcavity is formed. The cavity portion 27 of lower body member 11 receivesthe resistance unit 28 which comprises a rectangularly shaped mountingboard 29having a wire element 30 wound therearound. A wiper assembly 31is illustrated in Figure 4 and comprises a flat member 32 from which iscut a spring arm 33 terminating in a contact member 34. Wiper arms 35and 36 extend'from opposite sides of the member 32fand terminate in`flat sections carrying contacts 37 and 38, respectively. The ends 39and 4t) of member 32 are bent downward and contain V-shaped notches 41and 42, respectively. Thus, it is only necessary to drop the notches 41and 42 onto the threads of the shaft 18 in order to connect the wiperassembly to the shaft 18. Upon the rotation of the shaft, the threadswill engage the notched ends 39 and 40 and cause the wiper assembly 31to move along the shaft in a direction corresponding to the direction ofrotation of the shaft.

The surface of each of the cavities 27 contains a rectangular centergroove or slot 43 which extends the full length of the cavity 2.7 andeach slot 43 is crossed by grooves or slots 44, 45 and 46 whichextendgacross the cavity and connect, respectively, with slots 47, 48and 49 at one side of the cavity and with slots 47, 48 and 49 atV theother side of the cavity. Since the slot `45 `is located centrally ofthe body portions and the slots 44 and 46 are located equal distancesfrom the ends of the body portions, it is apparent that both the bodyportions can be constructed from the same tooling and placed together toprovide slots for leads which can extend to either side of the housing.One end of the winding 30 is connected to terminal lead 50 which is bentdownward to form a leg 51 and then outward to form a leg 52 and theninwardly, to form a leg 53. The leg 51 is located in the slot 49 of thebody portion 11, the leg 52 is located in the slot 46 of portion 11 andthe leg 53 is located in slot 43 of portion 11. A contact bead 54 islocated at the junction of legs 52 and 53 and bears aginst the wireelement 30. A second terminal lead 55 is located at the opposite end ofthe housing and is formed with legs 51', 52' and 53 which are receivedinthe slots 47, 44 and 43, respectively, of the body portion 11. Acontact bead 56 is located at the junction of legs 52' and 53' andengages the opposite end of the winding '30 to complete the circuitthrough the winding 30 and terminal leads 50 and 55. As illustrated inFigure 2, the legs 53 and 53 do not extend far enough to contact eachother in slot 43.

An output lead 57 is located centrally of the body portion and has a leg58 extending upwardly in slot 48 in the upper body portion 10 and has aleg extending through groove 45 of the upper body portion to connectwith strip 59 which extends the complete length of slot 43 of the bodyportion 10. As illustrated in 'Figure' 2, the contact 34 on spring arm33 moves along the strip 59 to continually connect the wiper assemblywith the' output lead 57 so that the output of this lead will vary withthe location of the wiper assembly on shaft 18.

The construction of the various components described above form animportant part of the present invention. The body portions 1i) and 11are preferably constructed of aluminum which has been anodized with ahard ceramic surface to insulate the body portions. By constructing thebody portions of aluminum or some similar metal, advantage can be talrenof the mechanical strength of the metal and of the good heat dissipationcharacteristics of the metal so that much higher operating temperaturesand power ratings can be obtained. Of course,v

other materials, such as plastics, can be utilized for the body portionsif so desired. The leads 50, 55 and 57 and the wiper assembly 31 arepreferably constructed of half hard beryllium copper having a gold flashon all surfaces so that these components incorporate very littleresistance in their circuits and resist corrosion. The member 25 canalso be constructed of beryllium copper, heat treated to full hardness,in order to have suicient spring properties to hold the end 24, of shaft18. As previously mentioned, the member 14 is constructed of nylon orother similar plastic material which retains good lubricatingproperties.

Themounting board 29 can be constructed of anodized aluminum or asuitable plastic and the surfaces of the wire are sprayed with aninsulating varnish so that long lengths of board can be wound and thencut to the desired siZ'e of the resistance unit. The wire 30 is buffedalong the path of the contacts 37 and 38 to remove the varnish andprovide good electrical connection and the lower surface of the wire isbulfed at locations to provide good connections with contacts 54 and 56.The body portions 10 and 11 are held together by adhesive 60 located attheir adjacent edges around the cavities 27 and this adhesiveaccomplishes the dual purpose of a mechanical connection and a humiditySeal. The adhesive 60 and the nylon member 14 seal all openings into theinterior of the potentiometer housing and thus, a low moisture conditioncan be maintained within the interior of the housing. The adhesive 60can `be subjected to induction heating in order to obtain a very strongbond between the body portions.

The manner in which the trimming potentiometer of the present inventioncan be assembled by simply placing one component after another together,will now be deh scribed. Starting with the body portion 11, the terminalleads 50 and 55 are first dropped into the slots in this portion and canbe held therein by adhesive if so desired. Thereafter, the resistanceunit 28 can be droppedinto the cavity `27 of the body portion 11 and thespring' member 25 can be inserted into the cutout 20 of the body portion11. Next, the shaft 18 is dropped onto the body portion 11 lSo thatmember 14 is located in cutoutsv 12 and 13 and spring member 25 issprung to receive slot 23 so that shaft end 22 can be located in cutout21. 'Ihe wiper assembly 31 can now be assembled on the shaft by simplydropping the notches 41 and 42 of the assembly onto the threads on theshaft 18. Thereafter, the output lead 57 can be assembled with the strip59 in the slot 43 of the body member 10 and adhesive 60 is appliedaround the edges of the two body members. After the portions and 11 areplaced together and secured by the adhesive, contact 34 will engagestrip 59 to provide an output reading from the potentiometer and thespring arm 33 will be flexed to hold the Wiper assembly on the threadsof shaft 18.

In operation of the device, the head member 14 can be rotated by anysuitable instrument or manually in order to vary the output signal. Thewiper assembly will be held in any set position because of the force ofspring arm 33 acting between the strip 59 and the notches 41 and 42.Also, when the wiper assembly abuts either end of the housing, one ofthe notched ends will be off the threads of shaft 18 (see dotted lineposition of Fig. 2) and the other notched end will skip over the threadssince the wiper assembly can move away from the threads by flexingspring arm 33. The spring member 25 serves to hold the shaft 18 in anyfixed position against vibrations and jiggling. In normal use, theterminal leads 50 and 55 will be connected in series with the windingelement 30 and the output lead 57 will carry an electrical signalcorresponding to the position of the wiper assembly 31. However, bysimply placing one of the terminal leads and the output lead 57 inseries with the winding 30, rotating of shaft 18 will select any desiredresistance for the circuit so that the instrument is easily convertibleinto a trimming resistor.

Referring to Figure 5, a modified element 14', constructed of suitablevplastic material, has an opening at one end for receiving the knurledend 17 of shaft 18 and the other end has a slot 19. A circular groove 61in the side of element 14 receives an O-ring 62 which bears againstV auniform` circular opening 12. 'I'he O-ring can be constructed ofneoprene or nylon to seal the opening 12. In the assembly of thismodification, the O-ring 62 will first be assembled in the groove 61prior to placing the shaft 18 onto the body portion 11.

The resistance' unit 28 is particularly adapted for the use of a varietyof resistance materials. In Figure 6 two strips 63 and 64 are shownattached along the length of the mounting board 29 and secured theretoby suitable adhesive. The elements 63 and 64 are located along thepathof the contacts 37 and 3S as they move along the resistance unitupon rotation of the member 14. In order to place these strips in theelectrical circuit of leads 50 and 55, silver clips 65 and 66 areplacedaround opposite ends of theboard 29 so that the upper sides of the clipscontact opposite ends of thestrips 63 and 64 and the lower surfaces ofthe clips extend inwardly sufficient so that clip 65 connects withcontact 54 and clip 66 connects with contact 56. Thus, the strips 63 and64 are connected in parallel with the leads 50 and 55. The versatilityA.of the resistanceunit is demonstrated by the fact that the strips 63and 64 can be formed of very thin strips of a high resistance metal,such as a nickel chrome alloy, which hashigh resistance properties andtheresistance rangewill vary-with the thickness of the strips. Also, thestrips 63 and 64 can comprise a pressure sensitive tape impregnated withthin flakes of carbon, such as carbon black, in order to produce aresistance. It is understood that the distance between the particles ofthe carbon on the tape can be varied to vary the resistance of the tapeper unit length. Thus, the mounting board 29 forms a convenient supportfor any suitable type of resistance material and if so desired, only onestrip of any desired width can be utilized. lt is apparent that thevarious forms of resistances can be used with any change in thecomponents of the instrument. Also, the silver clips 65 and 66 can bereplaced by beryllium copper clips with gold ash or with a silver paintcomposition which is conductive.

Referring to Figure 7, the mounting board 29 has mounted thereon thestrips 63 and 64 which can be constructed of the various materialspreviously described. In this embodiment of the invention, the strips 63and 64 are placed in series rather than in parallel with the terminalleads. The lead 50 has a short leg 52 in the slot 46 of body portion 11and this leg 52 is connected with one end of strip 64 by a layer ofconductive silver paint 67 which passes around to the end of themounting board 29. The opposite end of strip 64 is connected to theadjacent end of strip 63 by another layer 68 of conductive silver paint.The end of strip l63 opposite layer 68 connects with a layer of silverpaint 69 which passes over the end of the mounting board 29 and alongthe bottom of the mounting board to contact extended leg 52" of lead 55.It is understood that leg 52 will extend completely across the cavity 27in groove 44 and since the strips 63 and 64 are placed in series, alonger resistance is provided to give a greater potential drop. Becausethe contacts 37 and 38 on strips 63 and 64, respectively, will sensedifferent potentials, the output lead 59 will provide a signal which isa function of these two different potentials.

By the present invention a novel trimming potentiometer is providedwhich can be easily constructed in miniature size at minimum cost sinceall of the components are simply placed together one after another andthe hous ing is thereafter sealed to provide both a mechanical seal anda humidity seal. The potentiometer can be easily and quickly convertedinto a trimming resistor by placing either of the terminal leads inseries with the output lead through the winding element. Thepotentiometer has the feature that it is completely humidity tight sothat the resistance element is not affected by changes in the humidity.One important advantage of the invention is that the resistance elementsare assembled on a mounting board which is fabricated prior to assemblyand thus, a wide variety and assembly of the resistance elements can beutilized without changing the over-all construction of thepotentiometer. r[The novel assembly can be accomplished because of themanner in which the wiper assembly is connected with the shaft 18 andbecause of the manner in which the member 14 is constructed toautomatically compensate for moisture changes. Various modifications arecontemplated by those skilled in the art without departing from thespirit and scope of the invention as hereinafter `deined by the appendedclaims.

What is claimed is:

1. A potentiometer comprising a housing constructed of two body portionsof -identical construction, a cavity in each of said body portions lforforming a closed space within said housing when said body portions areplaced together, a plurality of grooves in the surface of each cavityfor receiving the leads for said potentiometer, each cavity having threegrooves leading to both sides of the cavity so that the body portionsare interchangeable and the lead located in each groove can bepositioned at either side of the housing.

2. A potentiometer as defined in claim l wherein each body portion has asemi-circular cutout at each end, said cutouts forming circular shaftsupporting openings at each end of said housing when said body portionsare placed together.

3. A potentiometer as defined in claim 2 having two terminal leads of aconfiguration substantially similar t0 said grooves in one body portion,resistance means carried by a mounting member of a configurationsubstantially similar to the cavity and positionable within the cavityof said one body portion over said two leads, a shaft having portions atopposite ends to be dropped into the semicircular cutouts of said onebody portion, a wiper assernbly movably carried on the shaft and havingnotched ends receivable onto thev threads of said shaft, and an' outputlead receivable into one of the grooves of the other body portioncooperating with said one body portion' to form said closed space.

4. A potentiometer as defined in claim 3l wherein each body portioncontains an'opening` at one end -t'oI form a second closed space incooperation with isaid? body portions, spring means received by saidopening in saidv one body portion, a notch in saidA spring means -toreceive one end of said shaft as. said shaft is positioned inthe cutoutsof said one body portion, said spring means being exed to receive saidone end of said shaft toliold the end of said shaft against a surface ofsaid second space.

5. A potentiometer as deiined in claim 3l having seal` ing andsupporting means attached to one end of said shaft, said sealing meansbeing located in one of said circular openings and extending exteriorlyof saidV housing.

6. A potentiometer comprising a housing constructed of twobody portions,a cavity in each ofsaid body portions dening a closed space within lsaidhousing-'when' said bodyp'ortio'ns are placed together,v"tv'voi-groov`es`A in the'cavity of one body portion and a thirdgr'ooveinfthe cavity of the other.bodyportion,,semicircula-cutouts at both endsof each body'memberlfor'ming a circular shaft supporting opening'at eachend of' said housing, two terminal leads having a similar coniiguration`to and receivable into the two grooves in saidl one body portion,resistance means carried by amounting member of similarconfiguration tothe cavityandreceivable into the cavity' of said one body portion oversaid two terminal leadsya'` shaft having portions at opposite ends -tobedropped into the cutouts of said one body portion, ay wiperassemblyhaving notched ends mounted onto` the threads of said shaft, and anoutput leadreceivable intosaidthird groove of said other body portioncooperating with said one body portion to form saidclosed space.

7. A potentiometer comprising a housing having an internal cavity, aresistance unit located within said cavity and connected at its endswith terminal leads extending exteriorly of said'housing, saidresistance unit comprising a flat mounting member extending along saidcavity for supporting a resistance means, movable means extending' intosaid cavity, a wiper assembly carried by said mov#v able means formovement along said resistance'means',l

andan output lead connected with said wiper assembly and extendingexteriorly of said housing, said resistance means comprisinga strip'ofresistance material attachedv along each edge of said mounting member,said wiper assembly having two contacts located at opposite sidesfof ingalong said oppositel side `for connecting the other strip to the otherterminal lead, and third conductive means connecting said stripstogether at the other end of said member' so that said strips are inSeries with said terminal leads. 10.-A Ipotentiometer. comprising ahousing having an internal cavity, a resistance unit located -withinsaid cav` ity, a'threaded `'shaft extending through said cavity, and awiper assembly `carried `by said shaft for movement along saidresistance unit pon'rotation of said shaft, said wiper assemblycomprising a body having two notched elements spaced apart to bereceived by the threads on said shaft and a Aspring arm carrying-acontact, said contact bearing against av lead extending along saidcavity in order to bias said elements against said threads and saidspring armvbeing ielribleto` permit either notched element to skip fromthread to-'thread after the other element has run off the threads at'one end of the shaft and into engagement with an end ofy said cavity.

11. A potentiometer comprising -a housing-having an internal cavity, aresistancev unit located withinsaid c'av ity and connected at its endswith terminal leads vembedded in one side of said cavity, a threaded'shaft extending throu'gh said cavity, means attached to one endy ofsaid shaft and extending through an opening at one end of said housingto` provide a bearing support and moisture seal, spring means attachedto the other end of lsaidshaft to hold vsaid other end in lixed positionagainst said housing and provide a dragon said` shaft, a wiper assemblycarried vb'ysaid shaft for movement along said resistance unit, saidwiper assembly comprising a body having two notched elements spacedapart to be received by the threads on said shaft and a spring armcarrying a contact, and an output lead embedded in the other side ofsaid cavity and extending along said cavity to continually engage saidcontactduring movement of said contact by rotation of said shaft, saidspring arm being exible to permitA either notchedjelement to skip fromthread to thread after the other element has saidvmountng member so thateach contact will move along one of said strips. y

8. A potentiometer as defined in claim 7 wherein said terminal leads arevlocated onv the opposite side of said mounting member from said strips,and conductive means passing around each end of said'niounting :memberto connect said strips inparallel `with "said terminal leads.

9. A potentiometer as defined vin claim 7 wherein said terminal leadsarel located lon the opposite side of saidv mounting member from saidstrips, irstconductive means, passing around one endv` of said memberfor connecting one strip to one terminal lead, second conductive meanspassing around'said one end of said member and extend.-I

run off the threads at one end of the shaft and into engagement with anend of said cavity.

12. A potentiometer as defined in claim 11 wherein said resistance unitcomprises resistance means carried by a` at mounting member extendingalong said cavity.

lReferences Cited in the le of this patent i UNITED STATES PATENTS1,371,049

OTHER REFERENCES Westinghouse Engineer, .lanuary 1947, pages 9 to 13.

